Golf ball

ABSTRACT

The invention provides a golf ball having a core and one or more cover layer encasing the core, wherein at least one cover layer is formed by injection-molding a single resin composition of primarily (A) a thermoplastic polyurethane and (B) a polyisocyanate compound, and at least some polyisocyanate compound in which all the isocyanate groups on the molecule remain in an unreacted state is present in the resin composition. The golf ball has a high rebound, an excellent spin performance and an excellent scuff resistance, and the cover layer-forming resin composition has excellent flow properties and an excellent cover layer manufacturability.

This is a continuation of application Ser. No. 11/507,534 filed Aug. 22,2006 now U.S. Pat. No. 8,182,367. The entire disclosure of the priorapplication, application Ser. No. 11/507,534, is considered part of thedisclosure of the accompanying continuation application and is herebyincorporated by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a golf ball in which a specificthermoplastic polyurethane material is used as the cover material. Morespecifically, the invention relates to a golf ball which has a highrebound, excellent spin characteristics and an excellent scuffresistance, and which is made using a thermoplastic polyurethanematerial having excellent flow properties and thus has an excellentmanufacturability.

The use of polyurethane materials as golf ball cover materials hasreceived attention in recent years. Polyurethane materials are broadlydivided, based on the process used to make molded parts therefrom, intothermoset polyurethane materials and thermoplastic polyurethanematerials. Molded parts made of thermoset polyurethane materials can beobtained by mixing under applied heat a urethane prepolymer havingisocyanate end groups with a liquid starting material such as a polyolor a polyamine as the curing agent, then pouring the mixture directlyinto a mold and heating to effect a urethane curing reaction.

Numerous golf balls which use such a thermoset polyurethane materialhave been disclosed in the prior art (e.g., Patent Reference 1: U.S.Pat. No. 5,334,673; Patent Reference 2: U.S. Pat. No. 6,117,024; andPatent Reference 3: U.S. Pat. No. 6,190,268). Methods of moldingthermoset polyurethane materials are described in, for example, PatentReference 4: U.S. Pat. No. 5,006,297; Patent Reference 5: U.S. Pat. No.5,733,428; Patent Reference 6: U.S. Pat. No. 5,888,437; Patent Reference7: U.S. Pat. No. 5,897,884; and Patent Reference 8: U.S. Pat. No.5,947,843.

Because moldings made of thermoset polyurethane materials lackplasticity when heated, the starting materials and molded parts cannotbe recycled. Moreover, given the length of the heating and curing stepand of the cooling step and given the great difficulty of controllingthe molding time owing to the high reactivity of the starting materialsunder heating and their instability, the manufacturability of moldedparts made of thermoset polyurethane materials, when used as specialtymoldings such as golf ball covers (moldings which encase a corematerial), is regarded as inefficient.

By contrast, moldings made of thermoplastic polyurethane materials arenot obtained by directly reacting the starting materials. Instead, alinear polyurethane material synthesized using starting materials and aproduction method which differ somewhat from those for the thermosetpolyurethane materials described above is employed in the moldingoperation. Such a polyurethane material is thermoplastic, andthermoplasticized polyurethane materials have the quality of solidifyingwhen cooled. Such polyurethane materials can thus be molded using aninjection molding machine. Injection molding a thermoplasticpolyurethane material requires a much shorter molding time than themolding time for a thermoset polyurethane material and moreover issuitable for precision molding, making it ideal as a process for moldinggolf ball covers. In addition, thermoplastic polyurethane materials arerecyclable, and are friendly to the global environment. Golf balls madeusing thermoplastic polyurethane materials are disclosed in, forexample, Patent Reference 9: U.S. Pat. No. 3,395,109; Patent Reference10: U.S. Pat. No. 4,248,432; and Patent Reference 11: U.S. Pat. No.4,442,282.

However, golf ball covers made with conventional thermoplasticpolyurethane materials have been unable to satisfy all of the followingproperties in a golf ball: feel on impact, controllability, rebound, andscuff resistance when hit with an iron.

To address this need, Patent Reference 12: JP-A 9-271538 discloses agolf ball cover made using a thermoplastic polyurethane material havinga high resilience. Yet, even this golf ball cover falls short in termsof its scuff resistance when hit with an iron.

Patent Reference 13: JP-A 11-178949 describes a golf ball cover whichhas a relatively good scuff resistance when hit with an iron and iscomposed primarily of the reaction product of a thermoplasticpolyurethane material with an isocyanate compound. In this cover, anisocyanate compound such as a block diisocyanate or an isocyanate dimeris added as an additive to the thermoplastic polyurethane material.Addition is carried out during melt mixing under applied heat using anextruder or during injection molding, with the reaction being effectedduring molding.

However, in the molding of a cover according to JP-A 11-178949 above,the isocyanate compound is hard to handle because it loses its activityin the presence of moisture, thus making it difficult to obtain a stablereaction product. In the case of blocked isocyanates, which are highlyresistant to moisture absorption, the blocking agent that dissociatesunder heating has a strong odor, making it unsuitable for use in moldingcovers. Moreover, when the isocyanate compound is in the form of apowder or a solution, it is difficult to control the amount of additionto the thermoplastic polyurethane material, making control of the golfball cover properties a challenge. Furthermore, owing to melting pointand melt viscosity differences between the thermoplastic polyurethanematerial and the isocyanate compound, slippage arises within the moldingmachine, which sometimes makes thorough kneading impossible to achieve.In this prior art, for the reasons given above, control of the effectsof moisture within the cover material and of the amount of additiveincluded therein has been inadequate, making it impossible to achievegolf ball covers which are fully satisfactory in terms of their scuffresistance-improving effects.

The preferred thermoplastic polyurethane material described in JP-A11-178949 is based on an aliphatic isocyanate. However, thisthermoplastic polyurethane material has a very high reactivity withisocyanate, making the reaction difficult to control. As a result, oneproblem is that gelation tends to arise before the mixture is used ininjection molding, making it impossible to ensure sufficient plasticity.Another problem is that gelation sometimes occurs during the moldingoperation. Yet another problem is that the resin to be recycledsometimes gels, as a result of which it cannot be reclaimed. Theseproblems have made it difficult to put the above technology to practicaluse.

Patent Reference 14: JP-B 58-2063 (U.S. Pat. No. 4,347,338) describes amethod of manufacturing thermoset polyurethane molded parts whichinvolves intimately mixing a compound having two or more isocyanategroups with a thermoplastic resin which does not react with isocyanategroups, blending the resulting mixture with a thermoplastic polyurethanematerial, then furnishing the blend to a molding machine and molding.However, the objects of this art are simply to improve the solventresistance and the resistance to continuous and repeated friction; thepublished specification makes no mention of the use of this moldingmaterial as a golf ball cover material. Accordingly, there continues toexist a desire for a golf ball cover material which can satisfy a numberof properties required of golf balls; i.e., rebound, distance, spincharacteristics, controllability, feel on impact, scuff resistance, cutresistance, and discoloration resistance.

Patent Reference 15: JP-A 2002-336378 discloses a golf ball which uses acover material composed of a thermoplastic polyurethane material and anisocyanate mixture. The cover material is a thermoplastic polyurethanematerial which is recyclable, has a high rebound, and has an excellentscuff resistance. Such a cover material has both a good thermoplasticpolyurethane manufacturability and exhibits physical propertiescomparable with those of thermoset polyurethanes. At the same time, theplasticizing effect of the isocyanate compound enhances the flowproperties of the thermoplastic polyurethane material, thus enabling themanufacturability to be improved as well. However, this excellent artalso has a number of drawbacks, including the generation of scorchedmaterial when the isocyanate mixture is charged directly into themolding machine, and variability in the mixing proportions due to theuse of a dry blending process, which results in a poor uniformity andleads to poor molding stability. In addition, because the relativeproportions within the isocyanate mixture of the isocyanate compound andthe thermoplastic resin which substantially does not react withisocyanate are already decided, it has been difficult to freely selectthe amounts and types of the isocyanate compound and the thermoplasticresin that one wishes to add.

In addition, Patent Reference 16: JP-A 2002-336380 describes a golf ballwherein a material obtained by blending a thermoplastic polyurethanematerial that contains as the polymeric polyol a polyether polyol havingan average molecular weight of at least 1500 and that has a reboundresilience of at least 40% with a specific isocyanate mixture is used asthe cover material. However, this cover material has the same drawbacksas those associated with the art disclosed in aforementioned PatentReference 15; namely, the generation of scorched material when the covermaterial is charged into the molding machine, poor molding stability,and limitations on selecting the amounts and types of isocyanatecompound to be added.

SUMMARY OF THE INVENTION

It is thus an object of the present invention to provide a golf ballhaving a high rebound and an excellent scuff resistance, which ball ismade using as the cover stock a thermoplastic polyurethane material ofexcellent flow properties and thus has excellent manufacturability.

The inventors have found that, in a golf ball composed of a core and oneor more cover layer, by using as the material making up at least onecover layer a molding of a resin composition of primarily (A) athermoplastic polyurethane and (B) a polyisocyanate compound, the golfball having this cover layer exhibits a higher rebound and excellentscuff resistance, in addition to which the cover resin material has ahigh fluidity, resulting in a high cover layer-formingmanufacturability. In particular, the inventors have found that byadditionally including (C) a thermoplastic elastomer other than athermoplastic polyurethane in the above resin composition and using amolding of the resin composition of (A) to (C) as the cover material,the above advantages can be effectively exhibited.

That is, on examining the role played by the addition of isocyanate to acover material composed primarily of a thermoplastic polyurethane, theinventors have learned that if the form of the isocyanate within thecover starting material is preserved so that the isocyanate groups arein an unreacted state, during injection molding, the plasticizing effectincreases the fluidity of the cover resin material, resulting in ahigher manufacturability and a higher degree of freedom in molding.Moreover, because a necessary and sufficient amount of unreactedisocyanate groups is present within the cover resin material, byinjection-molding this material under applied heat, crosslinkingreactions with component A occur, thus obtaining a golf ball having ahigh rebound and an excellent scuff resistance.

Accordingly, the invention provides the following golf balls.

-   [1] A golf ball comprising a core and one or more cover layer    encasing the core, wherein at least one cover layer is formed by    injection-molding a single resin composition of primarily (A) a    thermoplastic polyurethane and (B) a polyisocyanate compound, and at    least some polyisocyanate compound in which all the isocyanate    groups remain on the molecule in an unreacted state is present in    the resin composition.-   [2] The golf ball of claim 1, wherein the resin composition    additionally includes (C) a thermoplastic elastomer other than    thermoplastic polyurethane.-   [3] The golf ball of claim 2, wherein some of the isocyanate groups    in component B form bonds with active hydrogens in component A    and/or component C, and the other isocyanate groups remain in an    unreacted state within the resin composition.-   [4] The golf ball of claim 2, wherein the weight ratio (A):(B):(C)    of the respective components is 100:{2-50}:{0-50}.-   [5] The golf ball of claim 2, wherein the weight ratio (A):(B):(C)    of the respective components is 100:{2-30}:{8-50}.-   [6] The golf ball of claim 1, wherein the total weight of components    A and B combined is at most 90 wt %, of the overall weight of the    cover layer.-   [7] The golf ball of claim 1, wherein the resin composition has a    melt mass flow rate (MFR) at 210° C. of at least 5 g/10 min.-   [8] The golf ball of claim 1, wherein component B is one or more    polyisocyanate compound selected from the group consisting of    4,4′-diphenylmethane diisocyanate, 2,4-toluene diisocyanate,    2,6-toluene diisocyanate, p-phenylene diisocyanate, xylylene    diisocyanate, naphthylene-1,5-diisocyanate, tetramethylxylene    diisocyanate, hydrogenated xylylene diisocyanate,    dicyclohexylmethane diisocyanate, tetramethylene diisocyanate,    hexamethylene diisocyanate, isophorone diisocyanate, norbornene    diisocyanate, trimethylhexamethylene diisocyanate and dimer acid    diisocyanate.-   [9] The golf ball of claim 1, wherein component B is one or more    polyisocyanate compound selected from the group consisting of    4,4′-diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate    and isophorone diisocyanate.-   [10] The golf ball of claim 1, wherein component C is one or more    thermoplastic elastomer selected from the group consisting of    polyester elastomers, polyamide elastomers, ionomer resins, styrene    block elastomers, hydrogenated styrene-butadiene rubbers,    styrene-ethylene/butylene-ethylene block copolymers and modified    forms thereof, ethylene-ethylene/butylene-ethylene block copolymers    and modified forms thereof, styrene-ethylene/butylene-styrene block    copolymers and modified forms thereof, ABS resins, polyacetals,    polyethylenes and nylon resins.-   [11] The golf ball of claim 1, wherein component C is one or more    selected from the group consisting of polyester elastomers,    polyamide elastomers and polyacetals.

DETAILED DESCRIPTION OF THE INVENTION

The invention is described more fully below.

The golf balls of the invention have a core and one or more cover layerencasing the core. At least one of the cover layers is made of a moldedresin composition of primarily (A) a thermoplastic polyurethane and (B)a polyisocyanate compound. Such golf balls composed of a thermoplasticpolyurethane have an excellent rebound, spin performance and scuffresistance.

The cover layer is composed mainly of a thermoplastic polyurethane, andis formed of a resin composition of primarily (A) a thermoplasticpolyurethane and (B) a polyisocyanate compound.

To fully exhibit the advantageous effects of the invention, a necessaryand sufficient amount of unreacted isocyanate groups should be presentin the cover resin material. Specifically, it is recommended that thetotal weight of above components A and B combined be at least 60%, andpreferably at least 70%, of the overall weight of the cover layer.Components A and B are described in detail below.

The thermoplastic polyurethane serving as component A has a structurewhich includes soft segments made of a polymeric polyol that is along-chain polyol (polymeric glycol), and hard segments made of a chainextender and a polyisocyanate compound. Here, the long-chain polyol usedas a starting material is not subject to any particular limitation, andmay be any that is used in the prior art relating to thermoplasticpolyurethanes. Exemplary long-chain polyols include polyester polyols,polyether polyols, polycarbonate polyols, polyester polycarbonatepolyols, polyolefin polyols, conjugated diene polymer-based polyols,castor oil-based polyols, silicone-based polyols and vinyl polymer-basedpolyols. These long-chain polyols may be used singly or as combinationsof two or more thereof. Of the long-chain polyols mentioned here,polyether polyols are preferred because they enable the synthesis ofthermoplastic polyurethanes having a high rebound resilience andexcellent low-temperature properties.

Illustrative examples of the above polyether polyol includepoly(ethylene glycol), poly(propylene glycol), poly(tetramethyleneglycol) and poly(methyltetramethylene glycol) obtained by thering-opening polymerization of a cyclic ether. The polyether polyol maybe used singly or as a combination of two or more thereof. Of these,poly(tetramethylene glycol) and/or poly(methyltetramethylene glycol) arepreferred.

It is preferable for these long-chain polyols to have a number-averagemolecular weight in a range of 1,500 to 5,000. By using a long-chainpolyol having a number-average molecular weight within this range, golfballs made of a thermoplastic polyurethane composition having excellentproperties such as resilience and manufacturability can be reliablyobtained. The number-average molecular weight of the long-chain polyolis more preferably in a range of 1,700 to 4,000, and even morepreferably in a range of 1,900 to 3,000.

As used herein, “number-average molecular weight of the long-chainpolyol” refers to the number-average molecular weight computed based onthe hydroxyl number measured in accordance with JIS K-1557.

Suitable chain extenders include those used in the prior art relating tothermoplastic polyurethanes. For example, low-molecular-weight compoundswhich have a molecular weight of 400 or less and have on the moleculetwo or more active hydrogen atoms capable of reacting with isocyanategroups are preferred. Illustrative, non-limiting, examples of the chainextender include 1,4-butylene glycol, 1,2-ethylene glycol,1,3-butanediol, 1,6-hexanediol and 2,2-dimethyl-1,3-propanediol. Ofthese chain extenders, aliphatic diols having 2 to 12 carbons arepreferred, and 1,4-butylene glycol is especially preferred.

The polyisocyanate compound is not subject to any particular limitation;preferred use may be made of one that is used in the prior art relatingto thermoplastic polyurethanes. Specific examples include one or moreselected from the group consisting of 4,4′-diphenylmethane diisocyanate,2,4-toluene diisocyanate, 2,6-toluene diisocyanate, p-phenylenediisocyanate, xylylene diisocyanate, naphthylene-1,5-diisocyanate,tetramethylxylene diisocyanate, hydrogenated xylylene diisocyanate,dicyclohexylmethane diisocyanate, tetramethylene diisocyanate,hexamethylene diisocyanate, isophorone diisocyanate, norbornenediisocyanate, trimethylhexamethylene diisocyanate and dimer aciddiisocyanate. Depending on the type of isocyanate used, the crosslinkingreaction during injection molding may be difficult to control. In thepractice of the invention, to provide a balance between stability at thetime of production and the properties that are manifested, it is mostpreferable to use 4,4′-diphenylmethane diisocyanate, which is anaromatic diisocyanate.

It is most preferable for the thermoplastic polyurethane serving asabove component A to be a thermoplastic polyurethane synthesized using apolyether polyol as the long-chain polyol, using an aliphatic diol asthe chain extender, and using an aromatic diisocyanate as thepolyisocyanate compound. It is desirable, though not essential, for thepolyether polyol to be a polytetramethylene glycol having anumber-average molecular weight of at least 1,900, for the chainextender to be 1,4-butylene glycol, and for the aromatic diisocyanate tobe 4,4′-diphenylmethane diisocyanate.

The mixing ratio of activated hydrogen atoms to isocyanate groups in theabove polyurethane-forming reaction can be controlled within a desirablerange so as to make it possible to obtain a golf ball which is composedof a thermoplastic polyurethane composition and has various improvedproperties, such as rebound, spin performance, scuff resistance andmanufacturability. Specifically, in preparing a thermoplasticpolyurethane by reacting the above long-chain polyol, polyisocyanatecompound and chain extender, it is desirable to use the respectivecomponents in proportions such that the amount of isocyanate groups onthe polyisocyanate compound per mole of active hydrogen atoms on thelong-chain polyol and the chain extender is from 0.95 to 1.05 moles.

No particular limitation is imposed on the method of preparing thethermoplastic polyurethane used as component A. Production may becarried out by either a prepolymer process or one-shot process in whichthe long-chain polyol, chain extender and polyisocyanate compound areused and a known urethane-forming reaction is effected. Of these, aprocess in which melt polymerization is carried out in a substantiallysolvent-free state is preferred. Production by continuous meltpolymerization using a multiple screw extruder is especially preferred.

Illustrative examples of the thermoplastic polyurethane serving ascomponent A include commercial products such as Pandex T8295, PandexT8290, Pandex T8260, Pandex T8295 and Pandex T8290 (all available fromDIC Bayer Polymer, Ltd.).

Next, concerning the polyisocyanate compound used as component B, it iscritical that, in at least some of the polyisocyanate compound in thesingle resin composition, all the isocyanate groups on the moleculeremain in an unreacted state. That is, polyisocyanate compound in whichall the isocyanate groups on the molecule are in a completely free statemust be present within the single resin composition, and such apolyisocyanate compound may be present together with polyisocyanatecompound in which some of the isocyanate groups on the molecule are in afree state.

Various types of isocyanates may be employed without particularlimitation as this polyisocyanate compound. Illustrative examplesinclude one or more selected from the group consisting of4,4′-diphenylmethane diisocyanate, 2,4-toluene diisocyanate, 2,6-toluenediisocyanate, p-phenylene diisocyanate, xylylene diisocyanate,naphthylene-1,5-diisocyanate, tetramethylxylene diisocyanate,hydrogenated xylylene diisocyanate, dicyclohexylmethane diisocyanate,tetramethylene diisocyanate, hexamethylene diisocyanate, isophoronediisocyanate, norbornene diisocyanate, trimethylhexamethylenediisocyanate and dimer acid diisocyanate. Of the above group ofisocyanates, the use of 4,4′-diphenylmethane diisocyanate,dicyclohexylmethane diisocyanate and isophorone diisocyanate ispreferable in terms of the balance between the influence onprocessability of such effects as the rise in viscosity that accompaniesthe reaction with the thermoplastic polyurethane serving as component Aand the physical properties of the resulting golf ball cover material.

In the practice of the invention, although not an essential constituent,a thermoplastic elastomer other than the above-described thermoplasticpolyurethane may be included as component C together with components Aand B. Incorporating this component C in the above resin compositionenables the fluidity of the resin composition to be further improved andenables increases to be made in various properties required of golf ballcover materials, such as resilience and scuff resistance.

Component C, which is a thermoplastic elastomer other than the abovethermoplastic polyurethane, is exemplified by one or more thermoplasticelastomer selected from the group consisting of polyester elastomers,polyamide elastomers, ionomer resins, styrene block elastomers,hydrogenated styrene-butadiene rubbers,styrene-ethylene/butylene-ethylene block copolymers and modified formsthereof, ethylene-ethylene/butylene-ethylene block copolymers andmodified forms thereof, styrene-ethylene/butylene-styrene blockcopolymers and modified forms thereof, ABS resins, polyacetals,polyethylenes and nylon resins. The use of a polyester elastomer, apolyamide elastomer or a polyacetal is especially preferred for suchreasons as enhancing the resilience and scuff resistance while retaininga good manufacturability.

The relative proportions of above components A, B and C are not subjectto any particular limitation, although to fully achieve the advantageouseffects of the invention, it is preferable for the weight ratio(A):(B):(C) of the respective components to be 100:{2-50}:{0-50}, andmore preferably 100:{2-30}:{8-50}.

In the practice of the invention, the resin composition is prepared bymixing component A with component B, and additionally mixing alsocomponent C. It is critical to select the mixing conditions such that,of the polyisocyanate compound, at least some polyisocyanate compound ispresent in which all the isocyanate groups on the molecule remain in anunreacted state. For example, treatment such as the mixture in an inertgas (e.g., nitrogen) or in a vacuum state must be furnished. The resincomposition is then injection-molded around a core which has been placedin a mold. To smoothly and easily handle the resin composition, it ispreferable for it to be formed into pellets having a length of 1 to 10mm and a diameter of 0.5 to 5 mm. Isocyanate groups in an unreactedstate remain in these resin pellets; while the resin composition isbeing injection-molded about the core, or due to post-treatment such asannealing, the unreacted isocyanate groups react with component A orcomponent C to form a crosslinked material.

Various additives other than the ingredients making up theabove-described thermoplastic polyurethane may be optionally included inthe above resin composition. Additives that may be suitably used includepigments, dispersants, antioxidants, light stabilizers, ultravioletabsorbers and parting agents.

The melt mass flow rate (MFR) at 210° C. of the resin composition is notsubject to any particular limitation. However, to increase the flowproperties and manufacturability, the MFR is preferably at least 5 g/10min, and more preferably at least 6 g/10 min. Too low a melt mass flowrate reduces the fluidity, which may cause eccentricity during injectionmolding and may also lower the degree of freedom in the moldable coverthickness. The measured value of the melt mass flow rate is obtained inaccordance with JIS-K7210 (1999 edition).

The above method of molding the cover layer is exemplified by feedingthe above resin composition to an injection molding machine, andinjecting the molten resin composition around the core so as to form acover layer. The molding temperature varies according to such factors asthe type of thermoplastic polyurethane, but is typically in a range of150 to 250° C.

When injection molding is carried out, it is desirable though notessential to carry out molding in a low-humidity environment such as bypurging with a low-temperature gas using an inert gas such as nitrogenor low dew-point dry air or by vacuum treating some or all places on theresin paths from the resin feed area to the mold interior. Illustrative,non-limiting examples of the medium used for transporting the resininclude low-moisture gases such as low dew-point dry air or nitrogengas. By carrying out molding in such a low-humidity environment,reaction by the isocyanate groups is kept from proceeding before theresin has been charged into the mold interior. As a result,polyisocyanate in which the isocyanate groups are present in anunreacted state is included to some degree in the resin molded part,thus making it possible to reduce variable factors such as unwantedrises in viscosity and enabling the essential crosslinking efficiency tobe enhanced.

Techniques that could be used to confirm the presence of polyisocyanatecompound in an unreacted state within the resin composition prior toinjection molding about the core include those which involve extractionwith a suitable solvent that selectively dissolves out only thepolyisocyanate compound. An example of a simple and convenient method isone in which confirmation is carried out by simultaneousthermogravimetric and differential thermal analysis (TG-DTA) measurementin an inert atmosphere. For example, when the resin composition (covermaterial) used in the invention is heated in a nitrogen atmosphere at atemperature ramp-up rate of 10° C./min, a gradual drop in the weight ofdiphenylmethane diisocyanate can be observed from about 150° C. On theother hand, in a resin sample in which the reaction between thethermoplastic polyurethane material and the isocyanate mixture has beencarried out to completion, a weight drop from about 150° C. is notobserved, but a weight drop from about 230 to 240° C. can be observed.

After the resin composition has been molded as described above, itsproperties as a golf ball cover can be further improved by carryingannealing so as to induce the crosslinking reaction to proceed further.“Annealing,” as used herein, refers to aging the cover in a fixedenvironment for a fixed length of time.

At least one of the one or more cover layers on the inventive golf ballis made of the above-described thermoplastic polyurethane composition.The cover layer made of this thermoplastic polyurethane composition hasa surface hardness, expressed as the durometer D hardness, of generally30 to 90, preferably 35 to 85, more preferably 40 to 80, and even morepreferably 45 to 75. If the surface hardness of the cover layer is toolow, the spin rate when the ball is hit with a driver may increase,shortening the carry of the ball. On the other hand, if the surfacehardness of the cover layer is too high, the feel of the ball on impactmay worsen and the urethane material may have a poor resilience anddurability.

“Durometer D hardness” refers herein to the hardness measured with atype D durometer in accordance with JIS K7215.

The above-described cover layer has a rebound resilience of generally atleast 35%, preferably at least 40%, more preferably at least 45%, andeven more preferably at least 47%. Because a thermoplastic polyurethanedoes not inherently have that good a resilience, strict selection of therebound resilience is preferable. If the rebound resilience of the coverlayer is too low, the distance traveled by the golf ball maydramatically decrease. On the other hand, if the rebound resilience ofthe cover layer is too high, the initial velocity on shots of under 100yards that require control and on putts may be too high and the feel ofthe ball when played may not agree with the golfer. “Rebound resilience”refers herein to the rebound resilience obtained in accordance with JISK7311.

The core used in the inventive golf ball is not subject to anyparticular limitation. For example, various cores that may be usedinclude solid cores for two-pieces balls, solid cores having a pluralityof vulcanized rubber layers, solid cores having a plurality of resinlayers, and thread-wound cores having a rubber thread layer. Noparticular limitation is imposed on the diameter, weight, hardness,constituent materials and other characteristics of the core.

In cases where the golf ball of the invention has a construction thatincludes an intermediate layer, no particular limitation is imposed onthe hardness, constituent materials, thickness and other characteristicsof the intermediate layer. If necessary, a primer layer may be providedto improve adhesion between the intermediate layer and the cover.

It is preferable for the cover layer to have a thickness within a rangeof 0.1 to 5.0 mm. The cover layer is not limited to a single layer, andmay be formed with a multilayer construction of two or more layers. Ifthe cover is formed with a multilayer construction, the overallthickness of the cover may be set within the foregoing range.

The golf ball of the invention is preferably formed to a diameter andweight in accordance with the Rules of Golf, and is generally formed toa diameter of not less than 42.67 mm and a weight of not more than 45.93g. The diameter is preferably from 42.67 to 42.9 mm. It is suitable fordeflection by the ball when compressed under a load of 980 N (100 kg) tobe generally from 2.0 to 4.0 mm, and especially from 2.2 to 3.8 mm.

As explained above, the golf ball of the invention has a high rebound,excellent spin characteristics and scuff resistance, and the resincomposition used therein has high flow properties and an excellent coverlayer manufacturability.

EXAMPLES

The following Examples of the invention and Comparative Examples areprovided by way of illustration and not by way of limitation.

Examples 1 to 5, and Comparative Examples 1 to 3

Core Formulation:

Polybutadiene rubber 100 parts by weight Zinc diacrylate 24.5 parts byweight Zinc oxide 12 parts by weight Dicumyl peroxide 1 part by weightZinc pentachlorothiophenol 1 part by weight

The core material of the above formulation was kneaded, following whichit was molded and vulcanized at 155° C. for 20 minutes, therebyobtaining a 38.5 mm diameter solid core for a two-piece solid golf ball.The polybutadiene rubber used was BR01 produced by JSR Corporation. Theresulting core had a specific gravity of 1.17 g/cm³, a deflection of 3.4mm when compressed under a load of 980 N (100 kg), and an initialvelocity, measured in accordance with the measurement method of the USGA(R&A), of 78.1 m/s.

In Examples 1 to 5 of the invention, the starting materials shown inTable 1 (units: parts by weight) were worked in a twin-screw extruderand under a nitrogen gas atmosphere, thereby giving cover resincompositions. These resin compositions were in the form of pelletshaving a length of 3 mm and a diameter of 1 to 2 mm.

The solid core was placed within an injection-molding mold and the covermaterial was injection-molded around the core, thereby giving two-piecegolf balls in Examples 1 to 5 of the invention, each having a 2.1 mmthick cover. Samples for measuring the physical properties of the coverwere prepared by injection-molding a 2 mm thick sheet, annealing themolded sheet for 8 hours at 100° C., then holding the annealed sheet atroom temperature for one week. The manufacturability of the covermaterial was also evaluated. The results are shown in Table 1.

In Comparative Examples 1 and 2, the solid core was placed within aninjection-molding mold and a dry blend of thermoplastic polyurethanepellets with isocyanate mixture pellets was injection-molded around thecore, thereby giving two-piece golf balls having a 2.1 mm thick cover.Subsequent treatment was carried out in the same way as described abovefor the examples of the invention. In Comparative Example 3, onlypellets composed entirely of thermoplastic polyurethane wereinjection-molded, and annealing was not carried out.

TABLE 1 Example 1 2 3 4 5 Thermoplastic Polyurethane 1 100 polyurethanePolyurethane 2 100 100 100 100 (pbw) Polyisocyanate compound (pbw) 9 9 99 9 Thermoplastic elastomer (pbw) 15 15 15 15 15 Titanium oxide (pbw)3.5 3.5 3.5 3.5 3.5 Ultramarine blue (pbw) 0.4 0.4 0.4 0.4 0.4Polyethylene wax (pbw) 1.5 1.5 1.5 1.5 1.5 Montan wax (pbw) 0.8 0.8 0.80.8 0.8 MFR (at 210° C.) 7.8 8.0 8.0 8.0 8.0 Cover Surface hardness 5960 60 60 60 properties (D hardness) Rebound resilience 53 52 52 52 52(%) Ball Diameter (mm) 42.7 42.7 42.7 42.7 42.7 properties Weight (g)45.6 45.6 45.6 45.6 45.6 Hardness (mm) 2.3 2.3 2.2 2.3 2.3 Initialvelocity 77.1 77.1 77.1 77.1 77.0 (m/s) Scuff 23° C. 4 4 5 5 5resistance 13° C. 4 4 5 5 5  0° C. 3 4 4 4 4 Manufacturability good goodgood good good

TABLE 2 Comparative Example 1 2 3 Thermoplastic Polyurethane 3 100 0 100polyurethane Polyurethane 1 0 100 0 (pbw) Isocyanate mixture (pbw) 20 200 Titanium oxide (pbw) 3.5 3.5 3.5 Ultramarine blue (pbw) 0.4 0.4 0.4Polyethylene wax (pbw) 1.5 1.5 1.5 Montan wax (pbw) 0.8 0.8 0.8 MFR (at210° C.) 2.2* 2.4* 1.8 Cover Surface hardness (D hardness) 61 60 59properties Rebound resilience (%) 45 45 44 Ball Diameter (mm) 42.7 42.742.7 properties Weight (g) 45.7 45.7 45.7 Hardness (mm) 2.3 2.3 2.4Initial velocity (m/s) 77.1 77.1 77.0 Scuff resistance 23° C. 4 4 2 13°C. 4 4 2  0° C. 3 3 1 Manufacturability NG NG good *These are referencevalues; the cover material prepared was a mixture of different types ofpellets.Polyurethane 1 (Thermoplastic Polyurethane Material)

Pandex T8295, produced by DIC Bayer Polymer, Ltd.

Polyurethane 2 (Thermoplastic Polyurethane Material)

Pandex T8295 and Pandex T8290 were used in a weight ratio of 75/25. Bothare products of DIC Bayer Polymer, Ltd.

Polyurethane 3 (Thermoplastic Polyurethane Material)

Pandex T8260 and Pandex T8295 were used in a weight ratio of 50/50. Bothare products of DIC Bayer Polymer, Ltd.

-   Explanation of Pandex T8295: A MDI-PTMG-type thermoplastic    polyurethane material having a resin hardness of JIS-A97 and a    rebound resilience of 44%.-   Explanation of Pandex T8290: A MDI-PTMG-type thermoplastic    polyurethane material having a resin hardness of JIS-A93 and a    rebound resilience of 52%.-   Explanation of Pandex T8260: A MDI-PTMG-type thermoplastic    polyurethane material having a Durometer D resin hardness of 56 and    a rebound resilience of 45%.    Isocyanate Mixture

Crossnate EM-30 (an isocyanate masterbatch produced by DainichiseikaColor & Chemicals Mfg. Co., Ltd.; 4,4′-diphenylmethane diisocyanatecontent, 30%; the masterbatch base resin was a polyester elastomer).

Polyisocyanate Compound

4,4′-Diphenylmethane diisocyanate

Polyethylene Wax

Sanwax 161P, produced by Sanyo Chemical Industries, Ltd.

Montan Wax

Licowax E, produced by (Clariant Japan) K.K.

Thermoplastic Elastomer

A thermoplastic polyetherester elastomer (Hytrel 4001, produced byDuPont-Toray Co., Ltd.) was used.

Melt Mass Flow Rate (MFR)

The melt flow rate (or melt index) of the material was measured inaccordance with JIS-K7210 (test temperature, 210° C.; test load, 21 N(2.16 kgf)).

Surface Hardness of Cover Layer

The Durometer D hardness was measured in accordance with JIS-K7215.

Rebound Resilience of Cover Material

The rebound resilience was measured in accordance with JIS-K7311.

Ball Hardness (mm)

The deformation when compressed under a load of 980 N (100 kg) wasmeasured.

Ball Initial Velocity (m/s)

Measured in accordance with the measurement method of the USGA (R&A).

Scuff Resistance of Ball

The ball was held at respective temperatures of 23° C., 13° C. and 0° C.Using a swing robot machine, each ball was hit, using a pitching wedgeas the club, at a head speed of 33 m/s, after which damage from theimpact was visually rated according to the following criteria.

-   -   5: No damage whatsoever or substantially free of apparent        damage.    -   4: Slight damage is apparent, but of minimal concern.    -   3: Surface is somewhat frayed.    -   2: Surface is frayed and damaged dimples are apparent.    -   1: Some dimples are completely obliterated.        Ball Manufacturability    -   Good: Molding conditions during mass production were stable;        problems such as scorching of resin were infrequent.    -   NG: Molding conditions during mass production were unstable;        high frequency of problems such as resin scorching.

1. A golf ball comprising a core and one or more cover layers encasingthe core, wherein at least one cover layer is formed byinjection-molding a resin composition consisting essentially of (A) athermoplastic polyurethane, (B) a polyisocyanate compound, and (C) athermoplastic elastomer other than thermoplastic polyurethane, and atleast some polyisocyanate compound in which all the isocyanate groups onthe molecule remain in an unreacted state is present in the resincomposition, wherein the resin composition consists of a plurality ofthe same kind of pellets, wherein the pellets are formed from a mixtureof components (A), (B) and (C) as individual components, and wherein theat least one cover layer has a rebound resilience of at least 52%;wherein the weight ratio (A):(B):(C) of the respective components is100:{2-30}:{8-50}.
 2. The golf ball of claim 1, wherein some of theisocyanate groups in component B form bonds with active hydrogens incomponent A and/or component C, and the other isocyanate groups remainin an unreacted state within the resin composition.
 3. The golf ball ofclaim 1, wherein the total weight of components A and B combined is atmost 90 wt % of the overall weight of the cover layer.
 4. The golf ballof claim 1, wherein the resin composition has a melt mass flow rate(MFR) at 210° C. of at least 5 g/10 min.
 5. The golf ball of claim 1,wherein component B is one or more polyisocyanate compound selected fromthe group consisting of 4,4′-diphenylmethane diisocyanate, 2,4-toluenediisocyanate, 2,6-toluene diisocyanate, p-phenylene diisocyanate,xylylene diisocyanate, naphthylene-1,5-diisocyanate, tetramethylxylenediisocyanate, hydrogenated xylylene diisocyanate, dicyclohexylmethanediisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate,isophorone diisocyanate, norbornene diisocyanate, trimethylhexamethylenediisocyanate and dimer acid diisocyanate.
 6. The golf ball of claim 1,wherein component B is one or more polyisocyanate compound selected fromthe group consisting of 4,4′-diphenylmethane diisocyanate,dicyclohexylmethane diisocyanate and isophorone diisocyanate.
 7. Thegolf ball of claim 1, wherein component C is one or more thermoplasticelastomer selected from the group consisting of polyester elastomers,polyamide elastomers, ionomer resins, styrene block elastomers,hydrogenated styrene-butadiene rubbers,styrene-ethylene/butylene-ethylene block copolymers and modified formsthereof, ethylene ethylene/butylene-ethylene block copolymers andmodified forms thereof, styrene-ethylene/butylene-styrene blockcopolymers and modified forms thereof, ABS resins, polyacetals,polyethylenes and nylon resins.
 8. The golf ball of claim 1, whereincomponent C is one or more selected from the group consisting ofpolyester elastomers, polyamide elastomers and polyacetals.
 9. The golfball of claim 1, wherein some of the isocyanate groups in component Bform bonds with active hydrogens in component A, and the otherisocyanate groups remain in an unreacted state within the resincomposition.
 10. The golf ball of claim 1, wherein each of the pelletsof the resin composition has a length of 1 to 10 mm and a diameter of0.5 to 5 mm.
 11. The golf ball of claim 1, wherein the resin compositionis worked in an extruder and then is injection-molded, and wherein theunreacted isocyanate groups react with component A or component C toform a crosslinked material while the resin composition is beinginjection-molded.
 12. The golf ball of claim 1, wherein component B isisophorone diisocyanate.